Onboard diagnosis and correlation of failure data to maintenance actions

ABSTRACT

A method is provided for diagnosing a failure on an aircraft that includes aircraft systems configured to report faults to an onboard reasoner. The method includes receiving a fault report at an onboard computer of the aircraft from an aircraft system of the aircraft systems, the fault report indicating failed tests reported by the aircraft system. The onboard reasoner accesses an onboard diagnostic causal model represented by a graph describing known causal relationships between possible failed tests reported by the respective ones of the aircraft systems, and possible failure modes of the respective ones of the aircraft systems. The onboard reasoner diagnoses a failure mode of the aircraft system or another of the aircraft systems, from the failed tests, and using a graph-theoretic algorithm and the onboard diagnostic causal model. A maintenance action is determined for the failure mode, and a maintenance message is generated including the maintenance action.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/922,230, filed Dec. 9, 2019, entitled Onboard Diagnosis andCorrelation of Failure Data to Maintenance Actions, the content of whichis incorporated herein by reference in its entirety.

TECHNOLOGICAL FIELD

The present disclosure relates generally to aircraft maintenance and, inparticular, to onboard diagnosis of an aircraft system failure mode andrelated aircraft maintenance.

BACKGROUND

Complex systems such as machines including vehicles such as aircraft,spacecraft, watercraft, motor vehicles, railed vehicles, typicallyinclude some type of performance monitoring system that records dataregarding the machine performance, which includes the performance of thevarious systems (and subsystems) of the machine. The data include arecord of certain performance events that occur during the operation ofthe machine. The performance monitoring system typically conducts datacollection and reports all of the data collected to the user. The userthen may utilize the data in determining the type of maintenance orrepair, if any, that the machine may need. For example, if the dataindicates that a particular mechanical or electromechanical system ofthe machine is malfunctioning or that the performance of one or moremechanical or electromechanical systems may contribute to a futuremachine failure, then the user can perform the appropriate repair on themachine at the next opportunity.

While the current systems for machine performance and fault monitoringprovide the necessary data for a user to make an appropriate repairdecision, it is still necessary for a user to sort through all of thedata to determine the most-appropriate repair action to address a faultmode. Thus, the user must sort and interpret the data in light of theuser's knowledge of the particular machine. This can be time consumingand not always result in the first performed repair action being themost appropriate repair action, particularly for complex machines likeaircraft and other vehicles. For many types of machines, particularlycommercial vehicles, the amount of time the vehicle is out of service iscostly to the vehicle owner. As such, the longer it takes for themost-appropriate repair action to be performed for a given fault mode,the longer the vehicle will be out of service, which may be expensive tothe vehicle owner if the vehicle would otherwise be in service.

Therefore, it would be desirable to have a system and method that takesinto account at least some of the issues discussed above, as well asother possible issues.

BRIEF SUMMARY

Example implementations of the present disclosure are directed toimproved techniques for onboard diagnosis and correlation of failuredata to maintenance actions, and closed-loop diagnostic model maturationfor complex systems. Example implementations provide an onboard reasoneron an aircraft and a process for diagnosing a failure on the aircraft.Other example implementations provide an off-board reasoner and aprocess for closed-loop diagnostic model maturation in order to maintainthe onboard reasoner for diagnosing failures on the aircraft.

The present disclosure thus includes, without limitation, the followingexample implementations.

Some example implementations provide a method of diagnosing a failure onan aircraft that includes aircraft systems configured to report faultsto an onboard reasoner, the method comprising: receiving a fault reportat an onboard computer of the aircraft that includes the onboardreasoner, from an aircraft system of the aircraft systems, the faultreport indicating failed tests reported by the aircraft system;accessing, by the onboard reasoner, an onboard diagnostic causal modelrepresented by a graph that describes known causal relationships betweenpossible failed tests reported by the respective ones of the aircraftsystems, and possible failure modes of the respective ones of theaircraft systems; diagnosing, by the onboard reasoner, a failure mode ofthe aircraft system or another of the aircraft systems, from the failedtests, and using a graph-theoretic algorithm and the onboard diagnosticcausal model; determining a maintenance action for the failure mode; andgenerating, by the onboard computer, a maintenance message including atleast the maintenance action.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the onboard diagnostic causal model is represented bythe graph that includes nodes connected by edges, the nodes representingthe possible failed tests and the possible failure modes, and the edgesindicating the known causal relationships between the possible failedtests and the possible failure modes.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the onboard diagnostic causal model is represented bythe graph that is an assembly of graphs for respective ones of theaircraft systems, the graphs reflecting fault propagation behaviorwithin the respective ones of the aircraft systems, and the assemblyreflecting fault propagation behavior across connected ones of theaircraft systems.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the graph-theoretic algorithm is an optimal solutionset (OSS) algorithm.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the method further comprises sending the maintenancemessage to a display device onboard the aircraft, or a display device ona maintenance component configured to establish a connection with theonboard computer to receive the maintenance message.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, display of the maintenance message referencesinstructions for performing the maintenance action to address thefailure mode diagnosed by the onboard reasoner.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the fault report is one of a plurality of fault reportsof failed tests reported by respective ones of the aircraft systems, thefailure mode is one of a plurality of diagnosed failure modes of atleast some of the aircraft systems that caused the failed tests, and themethod further comprises: accessing diagnostic data received from theonboard computer, the diagnostic data including the plurality of faultreports and the plurality of diagnosed failure modes; accessing, by anoff-board reasoner, an off-board diagnostic causal model that describescausal relationships between the failed tests and the plurality ofdiagnosed failure modes, the off-board diagnostic causal model builtusing a graph-theoretic machine learning algorithm trained usinghistorical diagnostic data; comparing the diagnostic data to off-boarddiagnostic causal model; and based thereon, determining a new causalrelationship in the causal relationships described by the off-boarddiagnostic causal model that is new relative to the known causalrelationships; and updating the onboard diagnostic causal model tofurther describe the new causal relationship, including producing anupdated onboard diagnostic causal model, and uploading the updatedonboard diagnostic causal model to the onboard computer using a loadablesoftware airplane part upload tool set.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the diagnostic data further includes maintenancemessages with maintenance actions determined by the onboard reasoner forrespective ones of the plurality of diagnosed failure modes, and theonboard diagnostic causal model further describes relationships betweenthe possible failure modes and respective ones of the maintenanceactions, and wherein for a particular maintenance message with aparticular maintenance action for a respective diagnosed failure mode,the method further comprises: accessing a maintenance record with aperformed maintenance action and thereby a new maintenance action forthe respective diagnosed failure mode; and identifying a maintenanceaction discrepancy between the particular maintenance action and theperformed (new) maintenance action, to determine a new relationshipbetween the respective diagnosed failure mode and the performedmaintenance action, wherein updating the onboard diagnostic causal modelfurther includes updating the onboard diagnostic causal model todescribe the new relationship between the respective diagnosed failuremode and the performed (new) maintenance action.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the graph-theoretic machine learning algorithm is agraph-theoretic algorithm for finding maximal cliques.

Some example implementations provide an onboard computer for diagnosinga failure on an aircraft that includes aircraft systems configured toreport faults to an onboard reasoner, the onboard computer comprisingmemory configured to store computer-readable program code including theonboard reasoner; and processing circuitry configured to access thememory and execute the computer-readable program code to cause theapparatus to at least perform the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations.

Some example implementations provide a system for diagnosing a failureon an aircraft that includes aircraft systems configured to reportfaults to an onboard reasoner, the system comprising an onboard computerincluding the onboard reasoner configured to perform the method of anypreceding example implementation, or any combination of any precedingexample implementations.

Some example implementations provide a method of maintaining an onboardreasoner for diagnosing failures on an aircraft that includes aircraftsystems configured to report faults to the onboard reasoner, the methodcomprising: accessing diagnostic data received from an onboard computerof the aircraft that includes the onboard reasoner, the diagnostic dataincluding a plurality of fault reports of failed tests reported byrespective ones of the aircraft systems, and a plurality of diagnosedfailure modes of at least some of the aircraft systems that caused thefailed tests; building, using an off-board reasoner, an off-boarddiagnostic causal model that describes causal relationships between thefailed tests and the plurality of diagnosed failure modes, the off-boarddiagnostic causal model built using a graph-theoretic machine learningalgorithm trained using historical diagnostic data; comparing thediagnostic data to the off-board diagnostic causal model; and basedthereon, determine a new causal relationship in the causal relationshipsdescribed by the off-board diagnostic causal model that is new relativeto the known causal relationships; and updating the onboard diagnosticcausal model to further describe the new causal relationship, includingproducing an updated onboard diagnostic causal model, and uploading theupdated onboard diagnostic causal model to the onboard computer using aloadable software airplane part upload tool set.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the off-board diagnostic causal model is represented bya graph that includes nodes connected by edges, the nodes representingthe failed tests and the plurality of diagnosed failure modes, and theedges indicating the known causal relationships between the failed testsand the plurality of diagnosed failure modes.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the comparing of the diagnostic data to the off-boarddiagnostic causal model further comprises comparing to actual failuredata, diagnostic data, and maintenance action data collected from anonboard aircraft system, which reflect actual causal relationships.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the graph-theoretic machine learning algorithm is agraph-theoretic algorithm for finding maximal cliques.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the plurality of fault reports include a fault reportthat indicates those of the failed tests caused by a diagnosed failuremode of the plurality of diagnosed failure modes, and the method furthercomprises: diagnosing, by the off-board reasoner, a correspondingfailure mode of the aircraft system, from those of the failed testscaused by the diagnosed failure mode, and using the graph-theoreticmachine learning algorithm and the graph; and reporting any discrepancybetween the corresponding failure mode diagnosed by the off-boardreasoner, and the diagnosed failure mode of the plurality of diagnosedfailure modes from the diagnostic data received from the onboardcomputer.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the diagnostic data further includes maintenancemessages with maintenance actions determined by the onboard reasoner forrespective ones of the plurality of diagnosed failure modes, and theonboard diagnostic causal model further describes relationships betweenthe possible failure modes and respective ones of the maintenanceactions, and wherein for a particular maintenance message with aparticular maintenance action for a respective diagnosed failure mode,the method further comprises: accessing a maintenance record with aperformed maintenance action and thereby a new maintenance action forthe respective diagnosed failure mode; and identifying a maintenanceaction discrepancy between the particular maintenance action and theperformed maintenance action, to determine a new relationship betweenthe respective diagnosed failure mode and the performed maintenanceaction, wherein updating the onboard diagnostic causal model furtherincludes updating the onboard diagnostic causal model to describe thenew relationship between the respective diagnosed failure mode and theperformed maintenance action.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the method further comprises receiving a fault reportat the onboard computer of the aircraft that includes the onboardreasoner, from an aircraft system of the aircraft systems, the faultreport indicating failed tests reported by the aircraft system;accessing, by the onboard reasoner, the updated onboard diagnosticcausal model; diagnosing, by the onboard reasoner, a failure mode of theaircraft system or another of the aircraft systems, from the failedtests, and using a graph-theoretic algorithm and the updated onboarddiagnostic causal model; determining a maintenance action for thefailure mode; and generating, by the onboard computer, a maintenancemessage including at least the maintenance action.

In some example implementations of the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations, the graph-theoretic algorithm is an optimal solutionset (OSS) algorithm.

Some example implementations provide an off-board computer formaintaining an onboard reasoner for diagnosing failures on an aircraftthat includes aircraft systems configured to report faults to theonboard reasoner, the off-board computer comprising memory configured tostore computer-readable program code including an off-board reasoner;and processing circuitry configured to access the memory and execute thecomputer-readable program code to cause the off-board computer to atleast perform the method of any preceding example implementation, or anycombination of any preceding example implementations.

Some example implementations provide a system for maintaining an onboardreasoner for diagnosing failures on an aircraft that includes aircraftsystems configured to report faults to the onboard reasoner, the systemcomprising an onboard computer including the onboard reasoner and anoff-board computer including an off-board reasoner, the systemcomponents configured to perform the method of any preceding exampleimplementation, or any combination of any preceding exampleimplementations.

These and other features, aspects, and advantages of the presentdisclosure will be apparent from a reading of the following detaileddescription together with the accompanying figures, which are brieflydescribed below. The present disclosure includes any combination of two,three, four or more features or elements set forth in this disclosure,regardless of whether such features or elements are expressly combinedor otherwise recited in a specific example implementation describedherein. This disclosure is intended to be read holistically such thatany separable features or elements of the disclosure, in any of itsaspects and example implementations, should be viewed as combinableunless the context of the disclosure clearly dictates otherwise.

It will therefore be appreciated that this Brief Summary is providedmerely for purposes of summarizing some example implementations so as toprovide a basic understanding of some aspects of the disclosure.Accordingly, it will be appreciated that the above described exampleimplementations are merely examples and should not be construed tonarrow the scope or spirit of the disclosure in any way. Other exampleimplementations, aspects and advantages will become apparent from thefollowing detailed description taken in conjunction with theaccompanying figures which illustrate, by way of example, the principlesof some described example implementations.

BRIEF DESCRIPTION OF THE FIGURE(S)

Having thus described example implementations of the disclosure ingeneral terms, reference will now be made to the accompanying figures,which are not necessarily drawn to scale, and wherein:

FIG. 1 illustrates an aircraft according to some example implementationsof the present disclosure;

FIG. 2A illustrates a system for aircraft maintenance, according toexample implementations of the present disclosure;

FIG. 2B illustrates a block diagram of an onboard computer with anonboard reasoner functionally connected to an off-board computer with anoff-board reasoner, according to example implementations of the presentdisclosure;

FIG. 3 illustrates a graph-based representation of an onboard diagnosticcausal model, according to example implementations of the presentdisclosure;

FIG. 4 illustrates a sub-graph representing a maximal clique, accordingto example implementations;

FIGS. 5A, 5B, and 5C are flowcharts illustrating various steps in amethod of diagnosing a failure on an aircraft that includes aircraftsystems configured to report faults to an onboard reasoner, according toexample implementations;

FIGS. 6A, 6B, and 6C are flowcharts illustrating various steps in amethod of maintaining an onboard reasoner for diagnosing failures on anaircraft that includes aircraft systems configured to report faults tothe onboard reasoner, according to example implementations; and

FIG. 7 illustrates an apparatus according to some exampleimplementations.

DETAILED DESCRIPTION

Some implementations of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying figures, inwhich some, but not all implementations of the disclosure are shown.Indeed, various implementations of the disclosure may be embodied inmany different forms and should not be construed as limited to theimplementations set forth herein; rather, these example implementationsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. For example, unless otherwise indicated, reference something asbeing a first, second or the like should not be construed to imply aparticular order. Also, something may be described as being abovesomething else (unless otherwise indicated) may instead be below, andvice versa; and similarly, something described as being to the left ofsomething else may instead be to the right, and vice versa. Likereference numerals refer to like elements throughout.

Example implementations of the present disclosure are directed toimproved techniques for onboard diagnosis and correlation of failuredata to maintenance actions, and closed-loop diagnostic model maturationfor complex system. Example implementations provide an onboard reasoneron an aircraft and a process for diagnosing a failure on the aircraft.Additionally or alternatively, some example implementations provide anoff-board reasoner and a process for closed-loop diagnostic modelmaturation in order to maintain an onboard reasoner for diagnosingfailures on the aircraft.

FIG. 1 illustrates one type of aircraft 100 that may benefit fromexample implementations of the present disclosure. As shown, theaircraft includes an airframe 102 with a fuselage 104, wings 106 andtail 108. The aircraft also includes a plurality of high-level systems110 such as a propulsion system. In the particular example shown in FIG.1 , the propulsion system includes two wing-mounted engines 112. Inother embodiments, the propulsion system can include other arrangements,for example, engines carried by other portions of the aircraft includingthe fuselage and/or the tail. The high-level systems may also include anelectrical system 114, hydraulic system 116 and/or environmental system118. Any number of other systems may be included.

The high-level systems described above may include a plurality ofsensors and subsystems providing fault and sensor data that iscommunicated via an aircraft data communications bus network and/or anonboard network system (ONS) to an aircraft condition monitoring system(ACMS). The ACMS may collect, monitor, record and report real-timeaircraft system data, which may include error messages from a flightdeck effects (FDE) system, system test reports, fault reports and otherinformation. The data collected by the ACMS is used, for example, toperform cabin pressure and temperature monitoring, hard landingdetection, flight crew monitoring, and engine monitoring in addition tomany other aircraft performance functions. The received data is thenutilized to analyze aircraft performance, record significant flightevents, report aircraft system test reports and fault reports, andtroubleshoot faults.

The ACMS may be in communication with an onboard component/computer 120which may also be referred to as a central maintenance computer (CMC),on which may reside an aircraft health management or maintenancemanagement system and a diagnostic maintenance computing function(DMCF). The onboard computer 120 including the DMCF may receive aircraftsystem test reports and fault reports, and may further include anonboard diagnostic model. The DMCF may provide data acquisition for theonboard diagnostic model, which receives the test reports and faultreport data.

FIG. 2A illustrates a system 200 for maintenance of an aircraft 202 thatmay correspond to aircraft 100, according to some exampleimplementations. As described in greater detail below, the system mayinclude any of a number of different subsystems (each an individualsystem) for performing one or more functions or operations. Thesubsystems may be co-located or directly coupled to one another, or insome examples, various ones of the subsystems may communicate with oneanother across the one or more computer networks 204. Further, althoughshown as part of the system, it should be understood that any one ormore of the subsystems may function or operate as a separate systemwithout regard to any of the other subsystems. It should also beunderstood that the system may include one or more additional oralternative subsystems than those shown in FIG. 2A.

As shown, in some examples, the system 200 includes an onboard computer206 that may correspond to onboard component/computer 120. The onboardcomputer includes an onboard reasoner 208, and in some examples, theonboard computer is configured to diagnose a failure on the aircraftthat includes aircraft systems configured to report faults to theonboard reasoner. At least when the aircraft 202 corresponds to aircraft100, examples of suitable aircraft systems include propulsion system110, electrical system 114, hydraulic system 116 and/or environmentalsystem 118. Any number of other systems may be included.

In some examples, the onboard computer 206 is configured to receive afault report from an aircraft system of the aircraft systems, the faultreport indicating failed tests reported by the aircraft system. Theonboard computer is configured to access, by the onboard reasoner 208,an onboard diagnostic causal model, which may be represented by a graphthat describes known causal relationships between possible failed testsreported by the respective ones of the aircraft systems, and possiblefailure modes of the respective ones of the aircraft systems. In somemore particular examples, the onboard diagnostic causal model isrepresented by the graph that includes nodes connected by edges, inwhich the nodes represent the possible failed tests and the possiblefailure modes, and the edges indicate the known causal relationshipsbetween the possible failed tests and the possible failure modes.Additionally or alternatively, in some examples, the onboard diagnosticcausal model is represented by the graph that is an assembly of graphsfor respective ones of the aircraft systems, in which the graphs reflectfault propagation behavior within the respective ones of the aircraftsystems, and the assembly reflects fault propagation behavior acrossconnected ones of the aircraft systems.

With reference to FIG. 2B, the onboard computer includes an onboardreasoner 208, with which the onboard computer is configured to diagnosea failure on the aircraft that includes aircraft systems configured toreport faults to the onboard reasoner. The onboard computer 206 isconfigured to diagnose, by the onboard reasoner 208, a failure mode ofthe aircraft system or another of the aircraft systems, from the failedtests, and using the onboard diagnostic causal model 210 and agraph-theoretic algorithm such as an optimal solution set (OSS)algorithm. The onboard computer is also configured to generate a failurereport associated with the diagnosed failure mode, based on which amaintenance message may be generated that indicates a maintenanceaction. As shown in FIG. 2B, an off-board computer 218 is configured tomaintain the onboard reasoner 208. In some examples, the off-boardcomputer is configured to access diagnostic data received directly orindirectly from the onboard computer. This diagnostic data includes aplurality of fault reports of failed tests reported by respective onesof the aircraft systems, and a plurality of diagnosed failure modes ofat least some of the aircraft systems that caused the failed tests. Theoff-board computer 218 includes an off-board reasoner 224, which isconfigured to determine causal relationships between the failed testsand the plurality of diagnosed failure modes. The off-board diagnosticcausal model uses a machine learning algorithm trained using historicaldiagnostic data, which may be a machine learning algorithm such as agraph-theoretic algorithm for finding maximal cliques such as aBron-Kerbosch algorithm. The machine learning algorithm for findingmaximal cliques uses diagnostic data, including historical data thatrelates maintenance actions to maintenance messages or failure modes(obtained from a database of actual aircraft diagnostic data, whichincludes different failure modes; relationships between test reports,failure reports and components; maintenance action data, etc.), fordetermining known causal relationships between failure modes and failedtests. The off-board reasoner employing the machine learning algorithmis configured to use actual failure data, diagnostic data and/ormaintenance action data received from an onboard aircraft system (fromwhich to determine relationships between failure modes and failedtests), which is compared to the diagnostic data accessible from theaircraft onboard diagnostic system (onboard computer 206). The off-boardreasoner may determine a discrepancy based on the comparison, which maythen update and improve the onboard diagnostic causal model. Theidentification of a discrepancy may comprise identifying a newmaintenance action, from historical diagnostic data and maintenanceaction data collected from an aircraft onboard system, wherein thediscrepancy identification identifies a new maintenance action that isassociated with the failure mode.

FIG. 3 shows an example graph-based representation of an onboarddiagnostic causal model 300 suitable as the onboard diagnostic casualmodel 210, according to some example implementations. As shown, a faultreport 302 from an aircraft brake system antiskid wheelspeed transducer304 may indicate failed gear retract braking tests 306A, 306B. As alsoshown, the onboard diagnostic casual model may include nodes 308A-Cconnected by edges 310. The nodes may include nodes 308A, 308B thatrepresent the failed gear retract braking tests, and a node 308C thatrepresents a failure mode with a known causal relationship to the failedtests, as indicated by the edges connecting the nodes. In this regard,the failed tests share a common failure mode of a spurious operation ofthe aircraft brake system antiskid wheel speed transducer. This failuremode, then, may be diagnosed from the failed tests and using the onboardcausal model. A maintenance action may be implemented for the failuremode, and a maintenance message 312 that references instructions 314 forperforming the maintenance action may be generated. Such maintenanceaction data may be collected from the aircraft condition monitoringsystem or other system as historical maintenance action data and/ordiagnostic data, where actual historic diagnostic data and maintenanceaction data may be used in determining actual causal relationships.

Returning to FIG. 2A, the onboard computer 206 is configured todiagnose, by the onboard reasoner 208, a failure mode of the aircraftsystem or another of the aircraft systems, from the failed tests, andusing a graph-theoretic algorithm and the onboard diagnostic causalmodel 210. One example of a suitable graph-theoretic algorithm is anoptimal solution set (OSS) algorithm. The OSS algorithm may utilizesubmodular minimization of data to provide an efficient distributedoptimization algorithm, where data on various failed test reports may beassociated to an element or category of test reports or failure modes,and only data of subsets containing a specific failed test report orfailure mode itself is considered while ignoring all other data. Theoptimization algorithm may further create graphs of nodes forgraph-theoretic analysis, and may use neighboring node and/or edgeprobability analysis to determine a diagnosed failure mode, which woulddescribe a diagnosis causal relationship between failed tests reportedby the aircraft and possible failure modes for a reported aircraftsystem. The onboard computer is also configured to determine amaintenance action for the failure mode and generate a maintenancemessage 212 including at least the maintenance action.

In some examples, the onboard computer 206 is further configured to sendthe maintenance message 212 to a display device 214 onboard theaircraft, or to a display device on a maintenance component configuredto establish a connection with the onboard computer to receive anddisplay the maintenance message 212. In some of these examples, displayof the maintenance message references instructions 216 for performingthe maintenance action to address the failure mode diagnosed by theonboard reasoner 208.

As also shown in FIG. 2A, the system 200 in some examples includes anoff-board computer 218 configured to maintain the onboard reasoner 208.In some examples, the off-board computer is configured to accessdiagnostic data received directly or indirectly from the onboardcomputer. This diagnostic data includes a plurality of fault reports offailed tests reported by respective ones of the aircraft systems, and aplurality of diagnosed failure modes of at least some of the aircraftsystems that caused the failed tests.

As shown, in some examples, the system 200 includes at least one source220 of data. In some examples, the source includes a memory that may belocated at a single source or distributed across multiple sources. Thedata may be stored in a number of different manners, such as in adatabase or flat files of any of a number of different types or formats.In some of these examples, an aircraft condition monitoring system(ACMS) onboard the aircraft 202 may collect, monitor, record, and reportdiagnostic data. At least some of the diagnostic data may be accessiblefrom reports generated by the ACMS and may be wirelessly transmitted toa particular source of data—shown and at times referred to as anairplane health management (AHM) system 220A—directly or via anartificial satellite 222 or network(s) 204. In other of these examples,the diagnostic data may be transmitted via a wired connection orportable data storage device (e.g., flash memory, thumb drive).

In some examples, the off-board computer 218 includes an off-boardreasoner 224. The off-board computer is configured to build, using theoff-board reasoner, an off-board diagnostic causal model 226, which maybe that describes causal relationships between the failed tests and theplurality of diagnosed failure modes. The off-board diagnostic causalmodel is here built using a graph-theoretic machine learning algorithmtrained using historical diagnostic data. And in some examples, theoff-board diagnostic causal model is represented by the graph thatincludes nodes connected by edges, in which the nodes representing thefailed tests and the plurality of diagnosed failure modes, and the edgesindicating the known causal relationships between the failed tests andthe plurality of diagnosed failure modes. The offboard diagnostic causalmodel 226 employs a machine learning algorithm that uses failure data,historical diagnostic data and/or maintenance action data received froman onboard aircraft system. which is compared to diagnostic dataaccessible from the aircraft onboard diagnostic system (onboard computer206). The off-board diagnostic causal model 226 may determine adiscrepancy based its comparison to the diagnostic data. In the exampleonboard diagnostic causal model in FIG. 3 , a graph-based representationof a fault report 302 from an aircraft brake system antiskid wheelspeedtransducer 304 indicates failed gear retract braking tests 306A, 306B.The off-board diagnostic causal model 226 can identify a discrepancybased on collected maintenance action data such as a wheel speedtransducer repair instruction (MM_32_30710), for defining a newrelationship in the diagnostic causal model pertaining to the fault, tobe incorporated into the aircraft's onboard diagnostic reasoner model.

One example of a suitable graph-theoretic machine learning algorithm isa graph-theoretic algorithm for finding maximal cliques such as aBron—Kerbosch algorithm. A graph-theoretic machine learning algorithmfor finding maximal cliques may use diagnostic data to determine knowncausal relationships between failure modes and failed tests. FIG. 4shows diagnostic data and relationships may be transposed into a graphof a maximal clique 400 with nodes 402, 404, and edges 406 as describedbelow, one of each being called out in the figure. Here, the nodes 402represent possible failed tests T1, T2, T3, and T4, and the nodes 404represent possible failure modes F2, F4, F5, F8, and F10. The edgesindicate known causal relationships between the possible failed testsand the possible failure modes.

The maximal clique 400 can be determined from the graph, which in thisexample includes all of the nodes 402, 404 and edges 406 in the graphbased on the diagnostic data. In other examples a maximal clique mayinclude less than all of the nodes and edges. From the maximal clique,particular failure modes associated with failed tests may be isolated.

For example, the edges 406 may be examined to find the active failuremode(s) 404 associated with the reported failed tests at the nodes 402.The off-board reasoner 224 may determine that a clique is a maximalclique (e.g., maximal clique 400) if it has more than one node for afailed test. Further, the maximal clique may be identified as amonochromatic clique if all of the nodes for the failed tests have oneor more shared failure mode as determined from the edges connecting thenodes. A shared failure mode(s) becomes the failure mode of interest,and the monochromatic clique may then be used to identify the failedcomponent associated with the failure mode of interest. In FIG. 4 ,maximal clique 400 is a monochromatic clique with a shared failure modeF8 as identified from edges 404 connecting the nodes 402 representingthe failed tests with the nodes 404 representing the shared failure modeF8.

Returning again to FIG. 2A, the off-board diagnostic causal model 226may be matured by discovering any new relationships between failuremodes and failed tests that were not present in the onboard diagnosticcausal model 210 or are the result of emergent behavior in any of theaircraft systems. This can be mined from historical data that relatesmaintenance actions to maintenance messages 212 or failure modes, whichmay then update and improve the off-board diagnostic causal model.

The off-board diagnostic causal model 226 may have a certain signaturethat defines the expected propagation of the failure modes. Inoperation, the off-board reasoner 224 may record the portions of thesignature that it encounters while performing diagnosis. The off-boarddiagnostic causal model can be improved from this historical data (usinga historical signature), which can be compared to a previous off-boarddiagnostic causal model so that any new relationship can be consideredfor addition to an updated off-board diagnostic causal model.

The off-board computer 218 is configured to compare the diagnostic datafrom the onboard computer 206 to the off-board diagnostic causal model226 to diagnose failure modes of the aircraft systems. In this regard,the diagnostic data may describe known causal relationships betweenpossible failed tests reported by the respective ones of the aircraftsystems, and possible failure modes of the respective ones of theaircraft systems.

Based on the above, in these examples, the off-board computer 218 isconfigured to determine a new causal relationship in the causalrelationships described by the off-board diagnostic causal model 226that is new relative to the known causal relationships. The off-boardcomputer is also configured to update the onboard diagnostic causalmodel to further describe the new causal relationship. This includes theoff-board computer configured to produce an updated onboard diagnosticcausal model, and upload the updated onboard diagnostic causal model tothe onboard computer 206 as a loadable software airplane part (LSAP) viaan LSAP upload tool set 228.

In some examples, the plurality of fault reports include a fault reportthat indicates those of the failed tests caused by a diagnosed failuremode of the plurality of diagnosed failure modes. In some of theseexamples, the off-board computer 218 is further configured to diagnose,by the off-board reasoner 224, a corresponding failure mode of theaircraft system, from those of the failed tests caused by the diagnosedfailure mode, and using the graph-theoretic machine learning algorithmand the graph. The off-board computer, then, is also configured toreport any discrepancy between the corresponding failure mode diagnosedby the off-board reasoner, and the diagnosed failure mode of theplurality of diagnosed failure modes from the diagnostic data receivedfrom the onboard computer 206.

In some examples, the diagnostic data accessed by the off-board computer218 further includes maintenance messages 212 with maintenance actionsdetermined by the onboard reasoner 208 for respective ones of theplurality of diagnosed failure modes. In some of these examples, theonboard diagnostic causal model 210 further describes relationshipsbetween the possible failure modes and respective ones of themaintenance actions. For a particular maintenance message with aparticular maintenance action for a respective diagnosed failure mode,then, the off-board computer 218 is further configured to access amaintenance record with a performed maintenance action and thereby a newmaintenance action for the respective diagnosed failure mode. Theoff-board computer is also configured to identify a maintenance actiondiscrepancy between the particular maintenance action and the performedmaintenance action, to determine a new relationship between therespective diagnosed failure mode and the performed maintenance action.The new relationship may be a new maintenance action, which isidentified from historical diagnostic data and maintenance action datacollected from an aircraft, where the new maintenance action isassociated with the failure mode. And the off-board computer isconfigured to update the onboard diagnostic causal model to describe thenew relationship between the respective diagnosed failure mode and theperformed maintenance action. For example, the updated onboarddiagnostic causal model may further include the new maintenance actionthat is identified from collected historical maintenance action data,which is associated with the failure mode.

FIGS. 5A, 5B, and 5C are flowcharts illustrating various steps in amethod 500 of diagnosing a failure on an aircraft 202 that includesaircraft systems configured to report faults to an onboard reasoner 208,according to example implementations of the present disclosure.

As shown in FIG. 5A, at block 502, the method 500 includes receiving afault report at an onboard computer 206 of the aircraft 202 thatincludes the onboard reasoner 208, from an aircraft system of theaircraft systems, the fault report indicating failed tests reported bythe aircraft system. As shown at block 504, the method includesaccessing, by the onboard reasoner, an onboard diagnostic causal model210 represented by a graph that describes known causal relationshipsbetween possible failed tests reported by the respective ones of theaircraft systems, and possible failure modes of the respective ones ofthe aircraft systems.

As shown at block 506, the method includes diagnosing, by the onboardreasoner 208, a failure mode of the aircraft system or another of theaircraft systems, from the failed tests, and using a graph-theoreticalgorithm (e.g., an OSS algorithm) and the onboard diagnostic causalmodel 210. As shown at block 508, the method includes determining amaintenance action for the failure mode. And as shown at block 510, themethod includes generating, by the onboard computer 206, a maintenancemessage 212 including at least the maintenance action.

In some examples, the method 500 further includes sending themaintenance message 212 to a display device 214 onboard the aircraft202, or a display device on a maintenance component configured toestablish a connection with the onboard computer to receive themaintenance message, as shown at block 512.

As shown in FIG. 5B, in some examples the fault report is one of aplurality of fault reports of failed tests reported by respective onesof the aircraft systems, and the failure mode is one of a plurality ofdiagnosed failure modes of at least some of the aircraft systems thatcaused the failed tests. As shown at block 514, the method 500 furtherincludes accessing diagnostic data received from the onboard computer206, and the diagnostic data includes the plurality of fault reports andthe plurality of diagnosed failure modes.

As shown at block 516, the method 500 further includes accessing, by theoff-board reasoner 224, the off-board diagnostic causal model 226describing causal relationships between the failed tests and theplurality of diagnosed failure modes. The off-board diagnostic causalmodel is built using a graph-theoretic machine learning algorithmtrained using historical diagnostic data. The method further includescomparing the diagnostic data to the off-board diagnostic causal model,as shown at block 518.

Based on the comparison at block 518, the method 500 further includesidentifying a discrepancy between the diagnostic data and the off-boarddiagnostic causal model 226, to determine a new causal relationship inthe causal relationships described by the off-board diagnostic causalmodel 226 that is new relative to the known causal relationships, asshown at block 520. As shown at block 522, the method further includesupdating the onboard diagnostic causal model to further describe the newcausal relationship, including producing an updated onboard diagnosticcausal model, and uploading the updated onboard diagnostic causal modelto the onboard component using the LSAP upload tool set 228.

As shown in FIG. 5C, in some examples, the diagnostic data furtherincludes maintenance messages 212 with maintenance actions determined bythe onboard reasoner 208 for respective ones of the plurality ofdiagnosed failure modes, and the onboard diagnostic causal model 210further describes relationships between the possible failure modes andrespective ones of the maintenance actions. For a particular maintenancemessage with a particular maintenance action for a respective diagnosedfailure mode, the method 500 further includes accessing a maintenancerecord with a performed maintenance action and thereby a new maintenanceaction for the respective diagnosed failure mode, as shown at block 524.As shown at block 526, the method further includes identifying amaintenance action discrepancy between the particular maintenance actionand the performed maintenance action to determine a new relationshipbetween the respective diagnosed failure mode and the performedmaintenance action. The step of identifying a maintenance actiondiscrepancy may also include identifying a new maintenance action fromhistorical diagnostic data and maintenance action data collected from anaircraft condition monitoring system, wherein the discrepancyidentification identifies a new maintenance action that is associatedwith the failure mode. Then updating the onboard diagnostic causal modelfurther includes updating the onboard diagnostic causal model todescribe the new relationship between the respective diagnosed failuremode and the performed maintenance action, as shown at block 522A.

FIGS. 6A, 6B, and 6C are flowcharts illustrating various steps in amethod 600 of maintaining the onboard reasoner 208 for diagnosingfailures on the aircraft 202 that includes aircraft systems configuredto report faults to the onboard reasoner. As shown in FIG. 6A, at block602, the method includes accessing diagnostic data received from theonboard computer 206 of the aircraft that includes the onboard reasoner,the diagnostic data including a plurality of fault reports of failedtests reported by respective ones of the aircraft systems, and aplurality of diagnosed failure modes of at least some of the aircraftsystems that caused the failed tests.

As shown at block 604, the method 600 includes building, using anoff-board reasoner 224, an off-board diagnostic causal model 226 thatdescribes causal relationships between the failed tests and theplurality of diagnosed failure modes. The off-board diagnostic causalmodel is built using a graph-theoretic machine learning algorithmtrained using historical diagnostic data.

As shown at block 606, the method 600 includes comparing the diagnosticdata to the off-board diagnostic causal model 226. Based on thecomparison at block 606, the method 600 includes determining a newcausal relationship in the causal relationships described by theoff-board diagnostic causal model 226 that is new relative to the knowncausal relationships, as shown at block 608. As shown at block 610, themethod includes updating the onboard diagnostic causal model to furtherdescribe the new causal relationship, including producing an updatedonboard diagnostic causal model, and uploading the updated onboarddiagnostic causal model to the onboard computer using the LSAP uploadtool set 228.

In some examples, the plurality of fault reports include a fault reportthat indicates those of the failed tests caused by a diagnosed failuremode of the plurality of diagnosed failure modes, and as shown in FIG.6B, at block 612, the method 600 further includes diagnosing, by theoff-board reasoner 224, a corresponding failure mode of the aircraftsystem from those of the failed tests caused by the diagnosed failuremode, and using the graph-theoretic machine learning algorithm and thegraph. As shown at block 614, the method further includes reporting anydiscrepancy between the corresponding failure mode diagnosed by theoff-board reasoner and the diagnosed failure mode of the plurality ofdiagnosed failure modes from the diagnostic data received from theonboard computer 206.

In some examples, the diagnostic data further includes maintenancemessages 212 with maintenance actions determined by the onboard reasoner208 for respective ones of the plurality of diagnosed failure modes, andthe onboard diagnostic causal model 210 further describes relationshipsbetween the possible failure modes and respective ones of themaintenance actions. For a particular maintenance message with aparticular maintenance action for a respective diagnosed failure mode,as shown in FIG. 6C, the method 600 further includes accessing amaintenance record with a performed maintenance action and thereby a newmaintenance action for the respective diagnosed failure mode, as shownat block 616. The method further includes identifying a maintenanceaction discrepancy between the particular maintenance action and theperformed maintenance action, to determine a new relationship betweenthe respective diagnosed failure mode and the performed maintenanceaction, as shown at block 618. Then, updating the onboard diagnosticcausal model further includes updating the onboard diagnostic causalmodel to describe the new relationship between the respective diagnosedfailure mode and the performed maintenance action, as shown at block610A.

In some examples, the method 600 may tie into method 500 in which theupdated onboard diagnostic casual model may be used to diagnose afailure mode of an aircraft system. This may include receiving a faultreport at the onboard computer 206 of the aircraft 202 that includes theonboard reasoner 208 (see block 502). The onboard reasoner may accessthe updated onboard diagnostic causal model 210, and diagnose a failuremode of the aircraft system or another of the aircraft systems, from thefailed tests, and using a graph-theoretic algorithm and the updatedonboard diagnostic causal model (see blocks 504 and 506). A maintenanceaction for the failure mode may be determined, a maintenance message 212including at least the maintenance action may be generated (see blocks508 and 510).

According to example implementations of the present disclosure, thesystem 200 and its subsystems may be implemented by various means. Meansfor implementing the system and its subsystems may include hardware,alone or under direction of one or more computer programs from acomputer-readable storage medium. In some examples, one or moreapparatuses may be configured to function as or otherwise implement thesystem and its subsystems shown and described herein. In examplesinvolving more than one apparatus, the respective apparatuses may beconnected to or otherwise in communication with one another in a numberof different manners, such as directly or indirectly via a wired orwireless network 514 or the like.

FIG. 7 illustrates an apparatus 700 that in various exampleimplementations may be configured to implement the onboard computer 206and/or the off-board computer 218 shown in FIG. 2A. Generally, anapparatus of exemplary implementations of the present disclosure maycomprise, include or be embodied in one or more fixed or portableelectronic devices. Examples of suitable electronic devices include asmartphone, tablet computer, laptop computer, desktop computer,workstation computer, server computer or the like. The apparatus mayinclude one or more of each of a number of components such as, forexample, processing circuitry 702 (e.g., processor unit) connected to amemory 704 (e.g., storage device).

The processing circuitry 702 may be composed of one or more processorsalone or in combination with one or more memories. The processingcircuitry is generally any piece of computer hardware that is capable ofprocessing information such as, for example, data, computer programsand/or other suitable electronic information. The processing circuitryis composed of a collection of electronic circuits some of which may bepackaged as an integrated circuit or multiple interconnected integratedcircuits (an integrated circuit at times more commonly referred to as a“chip”). The processing circuitry may be configured to execute computerprograms, which may be stored onboard the processing circuitry orotherwise stored in the memory 704 (of the same or another apparatus).

The processing circuitry 702 may be a number of processors, a multi-coreprocessor or some other type of processor, depending on the particularimplementation. Further, the processing circuitry may be implementedusing a number of heterogeneous processor systems in which a mainprocessor is present with one or more secondary processors on a singlechip. As another illustrative example, the processing circuitry may be asymmetric multi-processor system containing multiple processors of thesame type. In yet another example, the processing circuitry may beembodied as or otherwise include one or more ASICs, FPGAs or the like.Thus, although the processing circuitry may be capable of executing acomputer program to perform one or more functions, the processingcircuitry of various examples may be capable of performing one or morefunctions without the aid of a computer program. In either instance, theprocessing circuitry may be appropriately programmed to performfunctions or operations according to example implementations of thepresent disclosure.

The memory 704 is generally any piece of computer hardware that iscapable of storing information such as, for example, data, computerprograms (e.g., computer-readable program code 706) and/or othersuitable information either on a temporary basis and/or a permanentbasis. The memory may include volatile and/or non-volatile memory, andmay be fixed or removable. Examples of suitable memory include randomaccess memory (RAM), read-only memory (ROM), a hard drive, a flashmemory, a thumb drive, a removable computer diskette, an optical disk, amagnetic tape or some combination of the above. Optical disks mayinclude compact disk—read only memory (CD-ROM), compact disk—read/write(CD-R/W), DVD or the like. In various instances, the memory may bereferred to as a computer-readable storage medium. The computer-readablestorage medium is a non-transitory device capable of storinginformation, and is distinguishable from computer-readable transmissionmedia such as electronic transitory signals capable of carryinginformation from one location to another. Computer-readable medium asdescribed herein may generally refer to a computer-readable storagemedium or computer-readable transmission medium.

In addition to the memory 704, the processing circuitry 702 may also beconnected to one or more interfaces for displaying, transmitting and/orreceiving information. The interfaces may include a communicationsinterface 708 (e.g., communications unit) and/or one or more userinterfaces. The communications interface may be configured to transmitand/or receive information, such as to and/or from other apparatus(es),network(s) or the like. The communications interface may be configuredto transmit and/or receive information by physical (wired) and/orwireless communications links. Examples of suitable communicationinterfaces include a network interface controller (NIC), wireless NIC(WNIC) or the like.

The user interfaces may include a display 710 and/or one or more userinput interfaces 712 (e.g., input/output unit). The display may beconfigured to present or otherwise display information to a user,suitable examples of which include a liquid crystal display (LCD),light-emitting diode display (LED), plasma display panel (PDP) or thelike. The user input interfaces may be wired or wireless, and may beconfigured to receive information from a user into the apparatus, suchas for processing, storage and/or display. Suitable examples of userinput interfaces include a microphone, image or video capture device,keyboard or keypad, joystick, touch-sensitive surface (separate from orintegrated into a touchscreen), biometric sensor or the like. The userinterfaces may further include one or more interfaces for communicatingwith peripherals such as printers, scanners or the like.

As indicated above, program code instructions may be stored in memory,and executed by processing circuitry that is thereby programmed, toimplement functions of the systems, subsystems, tools and theirrespective elements described herein. As will be appreciated, anysuitable program code instructions may be loaded onto a computer orother programmable apparatus from a computer-readable storage medium toproduce a particular machine, such that the particular machine becomes ameans for implementing the functions specified herein. These programcode instructions may also be stored in a computer-readable storagemedium that can direct a computer, a processing circuitry or otherprogrammable apparatus to function in a particular manner to therebygenerate a particular machine or particular article of manufacture. Theinstructions stored in the computer-readable storage medium may producean article of manufacture, where the article of manufacture becomes ameans for implementing functions described herein. The program codeinstructions may be retrieved from a computer-readable storage mediumand loaded into a computer, processing circuitry or other programmableapparatus to configure the computer, processing circuitry or otherprogrammable apparatus to execute operations to be performed on or bythe computer, processing circuitry or other programmable apparatus.

Retrieval, loading and execution of the program code instructions may beperformed sequentially such that one instruction is retrieved, loadedand executed at a time. In some example implementations, retrieval,loading and/or execution may be performed in parallel such that multipleinstructions are retrieved, loaded, and/or executed together. Executionof the program code instructions may produce a computer-implementedprocess such that the instructions executed by the computer, processingcircuitry or other programmable apparatus provide operations forimplementing functions described herein.

Execution of instructions by a processing circuitry, or storage ofinstructions in a computer-readable storage medium, supportscombinations of operations for performing the specified functions. Inthis manner, an apparatus 700 may include a processing circuitry 702 anda computer-readable storage medium or memory 704 coupled to theprocessing circuitry, where the processing circuitry is configured toexecute computer-readable program code 706 stored in the memory. It willalso be understood that one or more functions, and combinations offunctions, may be implemented by special purpose hardware-based computersystems and/or processing circuitry which perform the specifiedfunctions, or combinations of special purpose hardware and program codeinstructions.

Many modifications and other implementations of the disclosure set forthherein will come to mind to one skilled in the art to which thedisclosure pertains having the benefit of the teachings presented in theforegoing description and the associated figures. Therefore, it is to beunderstood that the disclosure is not to be limited to the specificimplementations disclosed and that modifications and otherimplementations are intended to be included within the scope of theappended claims. Moreover, although the foregoing description and theassociated figures describe example implementations in the context ofcertain example combinations of elements and/or functions, it should beappreciated that different combinations of elements and/or functions maybe provided by alternative implementations without departing from thescope of the appended claims. In this regard, for example, differentcombinations of elements and/or functions than those explicitlydescribed above are also contemplated as may be set forth in some of theappended claims. Although specific terms are employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

What is claimed is:
 1. An onboard computer for diagnosing a failure onan aircraft that includes aircraft systems configured to report faultsto an onboard reasoner, the onboard computer comprising: memoryconfigured to store computer-readable program code including the onboardreasoner; and processing circuitry configured to access the memory andexecute the computer-readable program code to cause the onboard computerto at least: receive a fault report from an aircraft system of theaircraft systems, wherein the fault report indicates failed testsreported by the aircraft system; access, by the onboard reasoner, anonboard diagnostic causal model represented by a graph that describesknown causal relationships between possible failed tests reported by therespective ones of the aircraft systems, and possible failure modes ofthe respective ones of the aircraft systems; diagnose, by the onboardreasoner, a failure mode of the aircraft system or another of theaircraft systems, from the failed tests, and using a graph-theoreticalgorithm and the onboard diagnostic causal model; determine amaintenance action for the failure mode; and generate, by the onboardcomputer, a maintenance message including at least the maintenanceaction; wherein the fault report is one of a plurality of fault reportsof the failed tests reported by respective ones of the aircraft systems,the failure mode is one of a plurality of diagnosed failure modes of atleast some of the aircraft systems that caused the failed tests; whereinthe onboard computer is further configured to send diagnostic dataincluding the plurality of fault reports and the plurality of diagnosedfailure modes; update the onboard diagnostic causal model to produce anupdated onboard diagnostic causal model and further describe a newcausal relationship; and upload the updated onboard diagnostic causalmodel to the onboard computer using a loadable software airplane partupload tool set.
 2. The onboard computer of claim 1, wherein the onboarddiagnostic causal model is represented by the graph that includes nodesconnected by edges, wherein the nodes represent the possible failedtests and the possible failure modes, and the edges indicate the knowncausal relationships between the possible failed tests and the possiblefailure modes.
 3. The onboard computer of claim 1, wherein the onboarddiagnostic causal model is represented by the graph that is an assemblyof graphs for respective ones of the aircraft systems, wherein thegraphs reflect fault propagation behavior within the respective ones ofthe aircraft systems, and the assembly reflects fault propagationbehavior across connected ones of the aircraft systems.
 4. The onboardcomputer of claim 1, wherein the graph-theoretic algorithm is an optimalsolution set (OSS) algorithm.
 5. The onboard computer of claim 1,wherein the processing circuitry is configured to execute thecomputer-readable program code to further cause the onboard computer to:send the maintenance message to a display device onboard the aircraft todisplay the maintenance message, or to a display device on a maintenancecomponent configured to establish a connection with the onboard computerto receive and display the maintenance message.
 6. The onboard computerof claim 5, wherein display of the maintenance message referencesinstructions for performing the maintenance action to address thefailure mode diagnosed by the onboard reasoner.
 7. A method ofdiagnosing a failure on an aircraft that includes aircraft systemsconfigured to report faults to an onboard reasoner, the methodcomprising: receiving a fault report at an onboard computer of theaircraft that includes the onboard reasoner, from an aircraft system ofthe aircraft systems, wherein the fault report indicates failed testsreported by the aircraft system; accessing, by the onboard reasoner, anonboard diagnostic causal model represented by a graph that describesknown causal relationships between possible failed tests reported by therespective ones of the aircraft systems, and possible failure modes ofthe respective ones of the aircraft systems; diagnosing, by the onboardreasoner, a failure mode of the aircraft system or another of theaircraft systems, from the failed tests, and using a graph-theoreticalgorithm and the onboard diagnostic causal model; determining amaintenance action for the failure mode; and generating, by the onboardcomputer, a maintenance message including at least the maintenanceaction; wherein the fault report is one of a plurality of fault reportsof the failed tests reported by respective ones of the aircraft systems,the failure mode is one of a plurality of diagnosed failure modes of atleast some of the aircraft systems that caused the failed tests, and themethod further comprises: accessing diagnostic data received from theonboard computer, the diagnostic data including the plurality of faultreports and the plurality of diagnosed failure modes; accessing, by anoff-board reasoner, an off-board diagnostic causal model that describescausal relationships between the failed tests and the plurality ofdiagnosed failure modes, the off- board diagnostic causal model builtusing a graph-theoretic machine learning algorithm trained usinghistorical diagnostic data; comparing the diagnostic data to theoff-board diagnostic causal model; and based thereon, determining a newcausal relationship in the causal relationships described by theoff-board diagnostic causal model that is new relative to the knowncausal relationships; and updating the onboard diagnostic causal modelto further describe the new causal relationship, including producing anupdated onboard diagnostic causal model, and uploading the updatedonboard diagnostic causal model to the onboard computer using a loadablesoftware airplane part upload tool set.
 8. The method of claim 7,wherein the onboard diagnostic causal model is represented by the graphthat includes nodes connected by edges, the nodes representing thepossible failed tests and the possible failure modes, and the edgesindicating the known causal relationships between the possible failedtests and the possible failure modes.
 9. The method of claim 7, whereinthe onboard diagnostic causal model is represented by the graph that isan assembly of graphs for respective ones of the aircraft systems, thegraphs reflecting fault propagation behavior within the respective onesof the aircraft systems, and the assembly reflecting fault propagationbehavior across connected ones of the aircraft systems.
 10. The methodof claim 7, wherein the graph-theoretic algorithm is an optimal solutionset (OSS) algorithm.
 11. The method of claim 7 further comprising:sending the maintenance message to a display device onboard the aircraftto display the maintenance message, or a display device on a maintenancecomponent configured to establish a connection with the onboard computerto receive the maintenance message.
 12. The method of claim 11, whereindisplay of the maintenance message references instructions forperforming the maintenance action to address the failure mode diagnosedby the onboard reasoner.
 13. The method of claim 7, wherein thediagnostic data further includes maintenance messages with maintenanceactions determined by the onboard reasoner for respective ones of theplurality of diagnosed failure modes, and the onboard diagnostic causalmodel further describes relationships between the possible failure modesand respective ones of the maintenance actions, and wherein for aparticular maintenance message with a particular maintenance action fora respective diagnosed failure mode, the method further comprises:accessing a maintenance record with a performed maintenance action forthe respective diagnosed failure mode; and identifying a maintenanceaction discrepancy between the particular maintenance action and theperformed maintenance action, to determine a new relationship betweenthe respective diagnosed failure mode and the performed maintenanceaction, wherein updating the onboard diagnostic causal model furtherincludes updating the onboard diagnostic causal model to describe thenew relationship between the respective diagnosed failure mode and theperformed maintenance action.
 14. The method of claim 7, wherein thegraph-theoretic machine learning algorithm is a graph-theoreticalgorithm for finding maximal cliques.
 15. A system for diagnosing afailure on an aircraft that includes aircraft systems configured toreport faults to an onboard reasoner, the system comprising: an onboardcomputer including the onboard reasoner, the onboard computer configuredto receive a fault report of the aircraft from an aircraft system of theaircraft systems, wherein the fault report indicates failed testsreported by the aircraft system, the onboard reasoner configured to:access an onboard diagnostic causal model represented by a graph thatdescribes known causal relationships between possible failed testsreported by the respective ones of the aircraft systems, and possiblefailure modes of the respective ones of the aircraft systems; anddiagnose a failure mode of the aircraft system or another of theaircraft systems, from the failed tests, and using a graph-theoreticalgorithm and the onboard diagnostic causal model, wherein the onboardcomputer is configured to determine a maintenance action for the failuremode, and generate a maintenance message including at least themaintenance action; wherein the fault report is one of a plurality offault reports of the failed tests reported by respective ones of theaircraft systems, the failure mode is one of a plurality of diagnosedfailure modes of at least some of the aircraft systems that caused thefailed tests, wherein the onboard computer is further configured to senddiagnostic data including the plurality of fault reports and theplurality of diagnosed failure modes, and wherein the system furthercomprises an off-board computer including an off-board reasoner, theoff-board computer configured to: access the diagnostic data receivedfrom the onboard computer; access, by the off-board reasoner, anoff-board diagnostic causal model that describes causal relationshipsbetween the failed tests and the plurality of diagnosed failure modes,the off-board diagnostic causal model built using a graph-theoreticmachine learning algorithm trained using historical diagnostic data;compare the diagnostic data to the off-board diagnostic causal model;and based thereon, determine a new causal relationship in the causalrelationships described by the off-board diagnostic causal model that isnew relative to the known causal relationships; and update the onboarddiagnostic causal model to further describe the new causal relationship,including the off-board computer configured to produce an updatedonboard diagnostic causal model, and upload the updated onboarddiagnostic causal model to the onboard computer using a loadablesoftware airplane part upload tool set.
 16. The system of claim 15,wherein the onboard diagnostic causal model is represented by the graphthat includes nodes connected by edges, wherein the nodes represent thepossible failed tests and the possible failure modes, and the edgesindicate the known causal relationships between the possible failedtests and the possible failure modes.
 17. The system of claim 15,wherein the onboard diagnostic causal model is represented by the graphthat is an assembly of graphs for respective ones of the aircraftsystems, wherein the graphs reflect fault propagation behavior withinthe respective ones of the aircraft systems, and the assembly reflectsreflecting fault propagation behavior across connected ones of theaircraft systems.
 18. The system of claim 15, wherein thegraph-theoretic algorithm is an optimal solution set (OSS) algorithm.19. The system of claim 15, wherein the onboard computer is furtherconfigured to send the maintenance message to a display device onboardthe aircraft to display the maintenance message, or a display device ona maintenance component configured to establish a connection with theonboard computer to receive the maintenance message.
 20. The system ofclaim 19 wherein display of the maintenance message referencesinstructions for performing the maintenance action to address thefailure mode diagnosed by the onboard reasoner.
 21. The system of claim15, wherein the diagnostic data further includes maintenance messageswith maintenance actions determined by the onboard reasoner forrespective ones of the plurality of diagnosed failure modes, and theonboard diagnostic causal model further describes relationships betweenthe possible failure modes and respective ones of the maintenanceactions, wherein for a particular maintenance message with a particularmaintenance action for a respective diagnosed failure mode, theoff-board computer is further configured to: access a maintenance recordwith a performed maintenance action for the respective diagnosed failuremode; and identify a maintenance action discrepancy between theparticular maintenance action and the performed maintenance action, todetermine a new relationship between the respective diagnosed failuremode and the performed maintenance action, and wherein the off-boardcomputer configured to update the onboard diagnostic causal modelincludes the off-board computer further configured to update the onboarddiagnostic causal model to describe the new relationship between therespective diagnosed failure mode and the performed maintenance action.22. The system of claim 15, wherein the graph-theoretic machine learningalgorithm is a graph-theoretic algorithm for finding maximal cliques.